Brain injury is a common and untreatable occurrence. Recently, however neurogenesis has been found in the adult mammalian brain. Much of the adult neurogenesis occurs in the subventricular zone (SVZ). The SVZ is a layer of mitotically active neuroblasts, glia, and progenitor cells that flank the lateral ventricles. SVZ cells have stem cell-like properties; when cultured in vitro they are capable of dividing indefinitely, and of differentiating into multiple cell types. The response of the SVZ to brain injury is poorly understood and understudied. These experiments will determine whether aspiration lesions of the sensorimotor cortex in mice, increase cell numbers, change the phenotype, change lineal fate restriction, or induce migration of cells out the SVZ and towards the site of lesion. Our Aim are: 1. To determine whether cortical lesions change the number of subventricular zone cells and/or the phenotype of newborn SVZ cells in adult mice. Cell numbers and BrdU incorporation will be quantified after unilateral aspiration lesions of the sensorimotor cortex in adult mice and compared to non-lesioned controls. Double immunofluorescence labeling for BrdU and phenotypic markers of cells in the SVZ will be analyzed with confocal microscopy to ascertain the identity of new-born cells after lesions. 2. To determine whether the fate restriction of cells in the SVZ changes after cortical lesions. We will infect SVZ cells with a replication incompetent retroviral library of degenerate oligonucleotides (BOLAP). The phenotypic restriction of clones will be determined with double immunofluorescence for viral epitopes and cell markers. Retrovirally labeled cells will be microdissected and their oligonucleotide inserts sequenced in order to serve as molecular tags of clonal identity. 3. To test the hypothesis that cortical lesions induce migration of cells out of the SVZ toward the lesion. BOLAP or DiI will be injected via ultrasound guidance directly into the SVZ or stereotactically into the lateral ventricle. We will analyze migration out of the SVZ towards the lesioned cortex. If cells migrate out of the SVZ then their phenotype will be ascertained by morphology and phenotype cell marker expression. In addition, structures immediately adjacent to the SVZ will be investigated for the re- emergence of radial glia-like fibers.